Phosphorus recovery by ion exchange in a solid carbonate: modeling of the process

Phosphorus (P) is a nutrient for plant growth but also a pollutant in water bodies causing eutrophication. The source of P is mainly human and animal wastewater and runoffs from different land uses. The objective of the present study is to evaluate P removal and recovery processes by ion exchange (IE) with solid carbonate (SC) in biodigestor-treated swine effluent (BTSE) using hydrogeochemical modeling. For this, BTSE compositions were obtained by literature review. A synthetized and characterized SC was used and the ion exchange site concentration ([SC-IE]) and the IE constants (K_ie) were obtained experimentally and applied to model P and major anion removal and recovery processes. P recovery was evaluated for different BTSE compositions and several concentrations of SC, dissolved P (HPO₄^2-), competing anions such as SO₄^2-, and CO₃^2-. The simulations suggest that a [SC-IE]:[HPO₄] of 1.4 molar ratio would allow the recovery of 90% of HPO₄ in BTSE, and at average alkalinity concentrations in BTSE, CO₃^2- would compete with HPO₄ for the SC-IE. The P recovery by the SC-IE process was compared with two other methods commonly used in P removal from BTSE: removal with aluminum sulfate and precipitation of struvite as a function of pH. The results suggest that SC-IE is the most efficient method in the pH range of BTSE. Besides, HPO₄^2- was readily recovered as inorganic P that may be reused in agriculture and industrial processes.

Sb(V) adsorption and desorption onto ferrihydrite: influence of pH and competing organic and inorganic anions

In this study, we investigated the Sb(V) adsorption on ferrihydrite (Fh) at different pH values, in the presence and absence of common competing anions in soil such as phosphate (P(V)) and arsenate (As(V)). Batch adsorption experiments, carried out at pH 4.5, 6.0, and 7.0, showed a greater affinity of Fh towards P(V) and As(V) with respect to Sb(V), especially at higher pH values, while the opposite was true at acidic pH. The capacity of Fh to accumulate greater amounts of phosphate and arsenate in the 6.0-7.0 pH range was mainly linked to the different acid properties of P(V), As(V), and Sb(V) oxyanions. The Sb(V) adsorption on Fh was highly pH-dependent and followed the following order: pH 4.5 (0.957 mmol·g^-1 Fh) > pH 6.0 (0.701 mmol·g^-1 Fh) > pH 7.0 (0.583 mmol·g^-1 Fh). Desorption of antimonate from Sb(V)-saturated Fh, treated with citric and malic acid solutions, was ~equal to 55, 68, and 76% of that sorbed at pH 4.5, 6.0, and 7.0, respectively, while phosphate, arsenate, and sulfate were able to release significantly lower Sb(V) amounts. The FT-IR spectra revealed substantial absorbance shifts related to the surface hydroxyl groups of Fh, which were attributed to the formation of Fe-O-Sb(V) bonds and supported the formation of inner-sphere bonding between Sb(V) and Fh.

Preferable uptake of phosphate by hydrous zirconium oxide nanoparticles embedded in quaternary-ammonium Chinese reed

Phosphate capture from aqueous was conducted using hydrous zirconium oxide (HZO) embedded in quaternary-ammonium Chinese reed (CR-N⁺-HZO), and the characteristics of adsorbent was determined. HZO was dispersed as nanoparticles or nano-clusters on the external or inside the networking pores of CR-N⁺-HZO. The surface of CR-N⁺-HZO was heterogeneous with multiple adsorption sites, HZO nanocomposite and N⁺(CH₂CH₃)₃Cl^-, which both contributed to the adsorption process. The phosphate uptake by CR-N⁺-HZO was optimal at pH 3.0 and phosphate uptake by HZO nanocomposite was greatly inhibited at alkaline pH. Kinetics studies suggested that both the intra-particle mass-transfer and external resistances were likely to be the rate controlling steps. The Q_max (maximum adsorption capacity) of phosphate uptake by CR-N⁺-HZO and CR-N⁺ (30°C) calculated based on Langmuir model was about 59.2mg(P)/g(CR-N⁺-HZO) and 30.4mg(P)/g(CR-N⁺). A high usage efficiency of Zr in CR-N⁺-HZO was observed with calculated molar ratio of P/Zr to be 3.07.